The present invention relates to implantable articles and methods of for implanting such articles. More particularly the invention relates to a bone prosthesis, prosthesis trial, instrument and method for implanting the same.
There are known to exist many designs for and methods for implanting implantable articles, such as bone prostheses. Such bone prostheses include components of artificial joints, such as elbows, hips, knees and shoulders.
One such implantable prosthesis is a shoulder prosthesis. During the life time of a patient, it may be necessary to perform a total shoulder replacement procedure on a patient as a result of, for example, disease or trauma, for example disease from osteoarthritis or rheumatoid arthritis. Currently, most implantable shoulder prostheses are total shoulder prostheses. In a total shoulder replacement procedure, a humeral component having a head portion is utilized to replace the natural head portion of the upper arm bone or humerus. The humeral component typically has an elongated intermedullary stem, which is utilized to secure the humeral component to the patient's humerus. In such a total shoulder replacement procedure, the natural glenoid surface of the scapula is resurfaced or otherwise replaced with a glenoid component that provides a bearing surface for the head portion of the humeral component.
In performing arthroplasties, the prosthesis, particularly for humeral prosthesis, have more recently been provided with humeral heads that are adjustable with respect to the stem portion of the prosthesis. Because of this adjustability, a trial head must first be used to determine what the correct position of the final implant should be. Adjusting the position of the trial head on the resected humeral bone may be difficult for at least two reasons. First, there may be a limited space in the surgical site. Such limited space is more of an issue in surgeries that utilize minimally invasive techniques where the incision lengths are somewhat shorter. If a surgeon must manipulate the position of the trial head with his hand, he may no longer have visibility to determine its correct position because his hand may block the view of the resected surface.
Adjusting the trial head is more of a problem for those surgeons who utilize a less invasive technique. Less invasive techniques where the incision length is shorter may not allow for enough space for the surgeon to use his hands to properly position the trial head. An additional issue with adjusting the trial head on the resected humeral bone is that the fluids typically found in the surgical site make the surgeon's latex glove very slippery. Without the use of the trial head handle, surgeons may have to hold onto the trial head with one hand while tightening the screw in the intermediate component, or neck, to lock the trial head with the other hand. If a surgeon is using an eccentric head and it inadvertently rotates, the direction of eccentricity may change. If the direction of eccentricity is changed, the final prosthesis will not be an accurate anatomical restoration of the humeral head as desired. Also, the torque generated by the twisting action in securing the components of the prosthesis may result in the humerus in patients with weak bones to approach the point of potential fracture.
Attempts have been made to provide shoulder prostheses with adjustability of the articulating head with respect to the distal stem. One such product uses a trial head to determine the position of the final implant. This product adjusts the positions of the trial head by placing a hex driver into holes on the side of the head. The technique is not optimal in that it is very difficult to adjust from the side because of the lack of space in the surgical site. If the surgeon cannot adjust the head properly, he may not get an exact anatomical restoration of the humeral head, or he may not be able to tighten the screws to lock the proper position. It may be also difficult to make the adjustment without damaging the soft tissue around the proximal humerus. Finally, the technique may be incompatible with less invasive approaches where access to the surgical site is limited due to small incisions.
The present invention attempts to overcome at least some of the aforementioned problems.